1. Industrial Field of the Invention
The present invention relates to a closed-type compressor having a structure taking a countermeasure against noise and vibration, a refrigerating unit, a refrigerator and an air conditioner each using the closed-type compressor.
2. Related Prior Art
A refrigerating unit such as a refrigerating showcase, a refrigerator or an air conditioner includes a refrigerating cycle having a compressor, a condenser, a pressure-reducing unit such as a capillary tube and the like which are disposed sequentially.
The compressor included in the refrigerating cycle, as shown in FIG. 18, has a closed casing 1 in which an electric motor 3 comprising a stator 2a and a rotor 2b and a compressing machine 5 connected to the motor 3 to be operated through a rotation shaft 4 are accommodated. The closed casing 1 is formed into a two-piece structure comprising a body case portion 6a formed into a cylindrical shape having a bottom and a cover case portion 6b for covering an opening portion of the body case portion 6a.
A refrigerator and an air conditioner, on each of which a compressor of the described type is mounted, are usually used in an ordinary home. Therefore, a great attention must be paid to take a countermeasure against noise as well as improving the performance of the compressor when the compressor is designed and manufactured. In particular, since the compressor acts as a critical noise generating source in the refrigerator and the air conditioner, there is a great desire for developing a compressor of a low noise type taking a countermeasure against noise into consideration.
The compressor has the closed casing in which the motor 3 and the compressing machine 5 are accommodated. The motor 3 and the compressing machine 5 act as sources for generating compressor noise. Noise generated in the motor 3 and compressing machine 5 is transmitted through the closed casing 1 or vibrates the closed casing 1. Therefore, in order to develop a low-noise type compressor, it is the easiest method to thicken the wall of the closed casing 1 and to thereby provide an excellent effect of preventing noise.
The closed casing 1 of the conventional compressor is formed into a two-piece structure comprising the body case portion 6a formed into a cylindrical shape having a bottom and the cover case portion 6b. The body case portion 6a is, by a deep drawing work, formed from a case material, i.e. a work, in the form of a disc plate shape into the cylindrical shape having a bottom. However, since the body case portion 6a is formed by the deep drawing work, the wall thickness of the casing and the length (the depth) of the drawn portion are limited to an unsatisfactory degree by the pressing performance of the pressing machine. If the wall of the body case portion 6a is intended to be thickened, considerably large pressing force is required and the machining accuracy is limited in thickening the wall of the body case portion 6a. Thus, there arises a problem in that a desired wall thickness of the case cannot be realized.
If the wall thickness of the body case portion 6a is intended to be thickened simply, a large-size pressing machine is required to perform the deep drawing work with a large machining force. In this case, the quantity of deformation of the work becomes too large, causing problems to arise in that galling takes place between a molding die and the work, breakage occurs due to damage of the work and the minimum wall thickness (the designed specification value) of the work cannot easily be maintained and therefore a satisfactory yield cannot be realized.
Since the refrigerator is usually installed in a room, the compressor noise must be severely prevented. In particular, noise in a low frequency range from 300 Hz to 500 Hz raises a problem of noise uncomfortable to persons and thus there arises a technical requirement to lower the noise in such low frequency range.
The low-frequency noise from the compressor is electromagnetic noise caused from the motor. A motor capable of fully preventing generation of the electromagnetic noise has not been designed yet. Although a program for designing the motor made on the basis of the motor efficiency, the torque and the manufacturing facility is present, no design program for preventing noise is present. Therefore, when a mounting test, in which the manufactured motor is mounted into a closed casing, is performed to examine the motor noise, the specifications, such as the motor coil wire, are changed to take a countermeasure against noise if excessive noise is generated in the motor.
However, the noise prevention means realized by changing the specifications of the motor coil or the like cannot satisfactorily prevent the low frequency noise of the compressor. There has arisen a requirement for a design for a closed-type compressor capable of satisfactorily preventing the low frequency noise.